An application server can be a server computer on a computer network dedicated to running certain software applications (as opposed to e.g. a file server or print server). Generally, an application server can be a software engine that delivers applications to client computers. In some cases, an application server can handle most, if not all, of the business logic and data access of the application. Benefits of application server technology can include the ease of application development and centralization. A J2EE application server refers to an application server that can comply with Java 2 Platform, Enterprise Edition (J2EE) standard.
An application server cluster, such as a WebLogic Server cluster, can consist of multiple application server instances running simultaneously and working together to provide increased scalability and reliability. A cluster can appear to clients to be a single application server instance. The server instances that constitute a cluster can run on the same machine, or be located on different machines. Users can increase a cluster's capacity by adding additional server instances to the cluster on an existing machine, or user can add machines to the cluster to host the incremental server instances.
IP Multicast is a technique for many-to-many communication over an IP infrastructure. It scales to a large receiver population by not requiring prior knowledge of whom or how many receivers there are. Multicast does not require a source sending to a given group to know about the receivers of the group. Multicast requires the source to send a packet only once. Unlike Multicast, Unicast is the sending of information packets to a single destination.